Most internal combustion engines today, and especially engines used for vehicle motivation, are equipped with catalytic exhaust converters for oxidizing unburned hydrocarbon fuel. Such converters are known to be highly efficient after being heated to an exhaust operating temperature of several hundred degrees Celsius. A problem exists, however, during the start-up and warm-up phases of engine operation. Because the engine is cold, combustion of the fuel/air mixture is sub-optimal, resulting in relatively high levels of unburned fuel in the exhaust, while simultaneously the exhaust catalyst is also sub-optimal cool and therefore ineffective or inefficient in oxidizing the abundant hydrocarbons in the exhaust.
It is known to use hydrogen enrichment of the fuel for an internal combustion engine to enable very low tailpipe emissions. Such a system is based on having an on-board catalytic fuel reformer for generating hydrogen-rich reformate from hydrocarbon-containing engine fuel. It is further known to fuel an engine upon start-up with a very fuel-lean reformate mixture (enabled by the wide flammability limits of reformate) while also supplying reformate directly to the engine exhaust. However, supplying reformate to both the engine intake and the engine exhaust simultaneously is a difficult challenge because of a significant pressure difference between these two locations. During engine idle, for example, in a spark ignition engine, a typical value for pressure in the engine intake is about 40 kPa, while a typical value of exhaust pressure is about 100–105 kPa. This difference becomes even greater as the air intake throttle is progressively opened, reducing intake manifold pressure and increasing exhaust manifold pressure.
It is further known to provide both a primary air pump for supplying primary air to the engine and a secondary air pump for supplying secondary air directly to the exhaust.
It is a principal object of the present invention to minimize exhaust emissions from an internal combustion engine during start-up and warm-up phases of engine operation.
It is a further object of the invention to minimize the cost and complexity of a system for controlling exhaust emissions during engine start-up and warm-up.
It is a still further object of the invention to provide such a system comprising a single air pump.